Illumination is used to light objects for seeing, as also for photography, microscopy, scientific purposes, entertainment productions (including theatre, television and movies), projection of images and as backlights of displays.
Furthermore, illumination is often required to be directed onto an object in a particular manner. For example, illumination sources for photography need to be diffused, illumination sources for backlights of displays need to be uniform and illumination sources for theatre spotlights need to be highly directional.
For illumination purposes, many systems provide point or single dimensional sources of light. Such systems have many drawbacks: light intensity is very high at the light source compared to the rest of the room or environment, and thus such light sources are hurtful to the eye. Such sources also cast very sharp shadows of objects, which are not pleasing to the eye, and may not be preferred for applications such as photography and entertainment production. Such sources also cause glare on surfaces such as table tops, television front panels and monitor front panels.
There are illumination systems that act as light sources in the form of a surface. Fluorescent lights for home lighting may be covered by diffuser panels to reduce the glare. These systems are bulky. They are also not transparent. Diffusers and diffuse reflectors such as umbrella reflectors are used as light sources for photography and cinematography, but they are only approximations to uniform lighting.
Illuminators in the form of a sheet emanating light in a particular emanation pattern have many applications. One such use is as a backlight for transmissive information displays. A backlight emanating light in a narrow viewing angle saves energy for personal viewing of displays, since lesser light energy is wasted in directions where a viewer is not present.
Systems that are light sources in the form of a surface, emanate light in a desired non uniform pattern. Such systems use optical films such as anisotropic scattering films. These systems are inefficient. Further, they render the light source non transparent.